Purification of gases.



F. G. COTTRELL. PURIIICATION 0I l GASES. Pruonlo'xrunp 11:13.26, 1909.RBNBWBD JULY 1, 1911.

f Purification of Gases, of which the followticles and then removingsuch cloud.

V.suspended in the gases and which form sulfur trioXid or sulfuric acidformed in the UNITED sTATEs PATENT oEEIcE.

FREDERICK GARDNER coTTRELI.,

0E BERKELEY, CALIFORNIA, AssIGNoR To INTER- NATIONALv PRECIPITATIONCOMPANY, 0F SAN FRAN CISCO, CALIFORNIA, A CORPO- RATION OF CALIFORNIA.

Patented Feb. 6, 1912.

Application led February 26, 1909, Serial No. 480,243. Renewed J'u1y 1,191i. Serial No. 636,514.

To all whom t may concern Be it known that I, FREDERICK GARDNERCoT'rRELL, a citizen of the United States, residing at Berkeley, in thecounty of Alameda and State of California, have invented certain new anduseful Improvements in ing is a specification. l

My invention relates to the art of purifying gases, and, especially tothose processes or methods which involve the production, in said gases,of a cloud of non-gaseous par- My invention is of special importance inthe purification of gases going to the cat-alyzing substances in thecontact process for manufacturing sulfuric anhydrid, and, eventuallysulfuric acid.

It is well known that the gases generated by .burning any of thecommercial forms of sulfur or sulfids, contain impurities such asselenium, tellurium, unburned sulfur, compounds of arsenic, organicmatter, etc., which destroy the activity of the platinum contact massorcatalyzer, which class of im purities will hereinafter be referred to asnoxious, in contradistinction to such ma-` terials as nitrogen, oxygen,sulfur trioxid and even small amounts of sulfuric acid, which are, bycontrast, innoxious as regards their action on the contact mass. Itis,also, generally conceded that these impurities tend to, concentratein'or on liquid particles mists, fogs or clouds. There is always someburners themselves which form clouds upon lowering the temperature. Ithas, therefore, been the endeavor, in most processes, to filter thegases at a moderate temperature as perfectly as possible before going tothe platinum contact substances, in orderl to remove any suspendedparticles' which they may contain. This is, sometimes, done without theintroduction of Water into the gases, as in the Mannheim process, and,sometimes, itis done after very thorough agitation with Water or steam,as in the Badische process. In such treatments it is,

sometimes, expedient to remove, by sedi-'l mentation or roughfiltratlon, the coarser l dirt from the gases before introducing theWater or steam and finally removing the finer particles or mist proper.

In order n'oW to understand my invention, the nature of which I shallpresently state, it must be noted that in all former practice, afteronce removing all the mist practicable, no attempt has been made toagain produce in the gases and subsequently remove therefrom a mist orcloud of suspended liquid particles for the purpose of purification, andstillvless to repeat this cycle of operation, until a given degree ofpurity is attained. In such repetition, Whether once or more than once,my invention is distinguished from all former practice; and mysaid'invention may, therefore, be stated, in general terms, to consistin causing successive formations and precipitations of nongaseousparticles in the gases to be purified.

As more specifically applied to burner gases in the contact sulfuricacid process, my invention consists, further, and more specifically, inartificially forming, by chemical reaction between gaseous constituentsout in the body of these gases a cloud of fine particles of puresulfuric acid, after the very impure acid resulting from hydration andcooling of the sulfurtrioxid, incidentallyv produced in the roastingprocess, has been removed, and then removing this cloud of fineparticles together with the residual impurities it has absorbed, by the.precipitating action of electric charges, and repeating this treatmentu'ith successive p0rtions of pure acid until the desired degree ofpurification is attained. The advantage of such successive treatment,over treatment in one step, even were the total amount of mi st` removedthe same in both cases, is analogous to that advantage obtained when.extracting a substance from 011e solvent by shaking with anothersolvent immiscible with the first, if we divide the second solvent intoa number of small portions and treat the first solvent with each ofthese portions successively', instead of using all ofthe second solventat once. The advantages of this procedure are too familiar to thoseacquainted with chemical technology,

'While my invention in its Ymost general c aspect is not'limited orconfined to any par- A pedient.

ticularcompositioi ofthe mist particles to be formed, 'still'as farascontact sulfuric acid plants jare concerned, sulfuric acid, formed thebody of the gas itself by the combination ofaqueous vapor and sulfurtriox'id,'is probably most convenient and ex- Nor is my invention, inits es sence, limited to any particular method or apparatus, either inthe formation or theremoval of the mist or cloud of suspended particles.I will, however, describe in de'- tail, as illustrative of theinvention,' the preferential method in a particular case, namely,- inthat of the gases, going to sulfur trioxid contact chambers, and, inthis confnection, I show an apparatus in the accom- 'panying drawings inwhich said method val by a second screen B2, and, at successiveintervals by two more screens B3 and B4. Above each 4of these screens isa feed-trough B, Fig. 2, to which water or weak.. sulfuric acid issupplied. The water or weak acid overflowing the troughs trickles downeach screen giving olf aqueous fvapor, and is received in underlyingdischarge troughs B-" which suitably dispose of it. jFollowmg each ofthe water or weak acid bearing screens, and separated from it'by arelatively small distance is another screen. There are four of thesedesignated by C1, C2, C3 and C4L respectively. Each of these screensis-supplied with fuming sulfuric acidfrom a feed trough C above, whichacid trickling down the screens gives off sulfur trioxid vapor, and isreceived in underlying discharge troughs C5. These screens may beconstructed of any suitable material.

^ Within the liuc A, in each space following the fuming acid-bearingscreens are mounted the'electrodes D and E. In each series oftheseelectrodes, there are electrodes D of one polarity, alternatingwith electrodes .E of the opposite polarity. The electrodes.

D are supported from bus-bars d resting on insulators d1, while theelectrodes E aresupported from bus-bars e 'resting directly upon thewalls of the line. Theelectrodes may conveniently receive their electriccharges from the high potential side of the step-up transformer T,through the intermittently contacting hub H driven by the synchronousmotor Ml such wise as to make contact at or near the peak of the voltagewave of the high. potential winding of the transformer-T, as more fullydiscussed in my United States Patent No, 859,729, Aug. 11, 1 908, theelectrodes E andflue wall being grounded, as indicated at G, for greatersafety. In the drawing `the bus- ."bars and electrical circuits are onlyshown for the last set of electrodes, it being understood that theothers may be connected in similar manner to the same source ofelectricity. These electrodes-D and E, by their discharges, precipitatethe mist. In this apparatus my process is carried out by bringing thegases in contact with the water or weak sulfuric acid on the vscreen B1,whereby aqueous vapor is supplied to them, followed immediately bycontact with the fuming acid on screen C1, thereby giving sulfurtrioxidto them, thus introducing by evaporation first gaseous water' andthen sulfur trioxid which react with one anotherin the body of the gasand produce a' fog, mist or cloud composed principally of particles ofsulfuric acid, the temperature of the gas being maintainedsuch thatalthough water and sulfur trioxid separately will readily evaporate, thesulfuric acid formed by their union in the gaseous state willimmediately condense as droplets ,of mist. A suitable temperature forthis process, as'the term is herein used is thus characterized. Theelectric charges upon the first series of electrodes D and E thenprecipitate the mist thus formed. The gases, then, passing on lto thelscreens B2 and'Cg, are again acted upon by the water and fuming acid,to reform the mist orv cloud, which is again pre cipitated by the`electric charges uponl the second series of electrodes D and E; and soon throughout the flue.

' If, in any given case, it should prove more convenient, the watervapor mayv be blown directly into the gases in the form of steam, andthe sulfur trioxid may likewise be drawn as gas directly from the mainscoming from the contact chambers, and delivnoxious material in saidgases and removing each such cloud of particles together with thenoxious impurities absorbed from the gas by its particles, before theformation of the next-succeeding cloud in the same mass of gas. Y

2.- The improvement in the art of purifying gases which consists inrepeatedly forming a cloud of non-gaseous particles of innoxiousmaterial in said gases, and removing, by electric charges, each suchcloud of particles vtogether With the noxious impurities absorbed fromthe gas by its particles, before the formation of the next succeedingcloud in the same mass of gas.-

3. The process of purifying the gases going to the contact mass in themanufacture of sulfur trioxid by the contact method which consists inrepeatedly forming a cloud of non-gaseous particles of innoxiousmaterial in said gases and removing each such cloud of particlestogether with the noxious impurities absorbed from the gas by itsparticles before the formation of the next succeeding cloud in the samemass lof g 4f. The process of purifying the gases going to the contactmass in the manufacture of sulfur trioxid by the contact method whichconsists in repeatedly forming a cloud of non-gaseous particles ofinnoxious material in said gases and removing each such cloud ofparticles together With the noxious impurities absorbed from` the gas byits lparticles by the application of electric. charges before theformation of the next succeeding cloud in the same mass of g 5. Thatstepin the purification of the gases going to the contact mass in theman'- ufacture of sulfur trioxid by the contact method Which consists inproducing in said gases at a suitable temperature a cloud of suspendedparticles of sulfuric acid after said gases have been freed fromsubstantially. all sulfuric acid and other suspended particles whichthey may have previously contained, and thereby absorbing by saidparticles noxious impurities still contained in said gases.

6. That step in thel purification ofthe gases going to the contact massin the manufacture of sulfur trioxid by the contactmethod which consistsin bringing said gases at a suitable temperature into contact with aliquid giving off sulfur trioxid vapor and another liquid giving offWater vapor for the purpose of producing a cloud of suspended particlesof sulfuric acid .in said gases, and thereby absorbing by said particlesnoxious impurities still contained in said gases.

7. The process of purification of the gases going to the contact mass inthe manufacture of sulfur trioxid by the contact method `Which consistsin producing in said gases, at a suitable temperature, a lcloud ofsuspended particles of sulfuric acid after said gases have been freedfrom substantially all sulfuric acid and other suspended` particlesWhich they may have previously contained, and finally removing saidartificially produced cloud of sulfuric acid parof sulfuric acid haveabsorbed.

8. The process of purification of the gases going to the contact mass inthe manufacture of sulfur trioxid bythe contact method which consists inproducing in said gases, at a `suitable temperature, la cloud ofsuspended particles of sulfuric acid after said gases have been freedfrom substantially all sulfuric acid and other suspended particles Whichthey may have previously containedl and thereby absorbing by saidparticles noxious impurities still contained in said gases; thenremoving said artificially produced cloud of sulfuric acid particlestogether with said noxious impurities thus absorbed, from said gases;and then repeating t-he alternate production and removal of saidsuspended particles until the desired degree of purification isattained.

9. The process of purification of the gases going to the contact mass inthe manufacture of sulfur trioxid by the contact method Which consistsin producing in said gases, at a suitable temperature, a cloud ofsuspended particles of sulfuric acid after said gases have been freedfrom substantially all sulfuric acid and other suspended particles whichthey may have previously contained, and finally removing saidartificially produced cloud of sulfuric acid particles from said gasestogether With the noxious impurities of said gases which said particlesof sulfuric acid have absorbed by the application of electric charges.

l0. The process of.f purification of the gases going to the contact massin the manufacture of sulfur trioxid by the contact method whichconsists in producing in said gases, at a suitable temperature, a cloudof suspended particles of sulfuric acid after said gases have been freedfrom substantially all sulfuric acid and other suspended particleswhichl they may .have previously contained and thereby absorbing by saidparticles'noxious impurities still contained in said gases then removingsaid lartificially produced cloud of sulfuric acid particles togetherwith said noxious impurities from said gases by the applicationofelectric charges; and then repeating the alternate production andremoval of said suspended particles until the desired degree ofpurlcation is attained.

l1. The process. of purification of the gases going to the contact massin the/man.-

ufacture of sulfur trioxid by the contact method which consists inbringing said gases at a suitable temperature into contact with a liquidgiving oli lsulfur trioxid vapor and with another liquid giving ofi'I Waer vapor for the purpose of producing acloud of suspended particles ofsulfuric acid in said gases after said gaseshave been freedy fromsubstantially all sulfuric acid and other suspended particles which theymay have previously contained thereby absorbing by said particlesnoxious particles still contained in said gases; then removing saidartificially produced cloud of sulfuric acid particles from said gasestogether with said noxious impurities thus absorbed m the application ofelectric charges; and

10 then repeating this alternate production and removal of suspendedfparticles until the desired degree of puri cation is attained.

In testimony whereof I have signed my name to this specification in thepresence l5 of two subscriblng witnesses.

FREDERICK GARDNER COTTRELL. Witnesses:

WM. F. BOOTH, D. B. RICHARDS.

